This invention relates generally to fibers and fabrics prepared from crystalline propylene polymer compositions comprising both propylene homopolymer and propylene copolymer components. Preferably the propylene polymer composition is isotactic. The compositions are prepared using metallocene catalyst systems in a polymerization process that involves the sequential or parallel polymerization of propylene homopolymer and copolymer using propylene with a small amount of comonomer, preferably ethylene. The resulting polymer compositions are excellent for use in the production of fibers and fabrics. Fibers prepared with these propylene polymers are substantially more elastic, and fabrics prepared with these polymers are stronger, softer have a higher elongation and have a significantly broader and lower bonding window at lower temperatures compared to fibers and fabrics prepared from known propylene-based polymers. The broader bonding window is especially advantageous when bonding heavy basis weight fabrics.
Propylene polymer fibers and fabrics are widely used in many applications including twine, carpet, medical gowns and drapes, and diapers. The optimization of processing characteristics and properties of propylene based fibers and fabrics has been the subject of intense effort. For example, WO 94/28219 and U.S. Pat. No. 5,637,666 describe fibers and fabrics prepared from metallocene catalyzed isotactic polypropylene. These fibers are significantly stronger compared to fibers prepared with Ziegler-Natta catalyzed isotactic polypropylene.
The present inventors have discovered that crystalline propylene polymer compositions made by polymerizing propylene in one stage and then propylene and a minor amount of comonomer in a separate stage using a metallocene catalyst system results in polymers which impart improved elasticity, strength, and processing characteristics when used to make fibers and fabrics.
Multiple stage polymerization processes are known in the art and are usually used to prepare block copolymers which contain rubbery materials as opposed to the crystalline polymers of this invention. U.S. Pat. Nos. 5,280,074; 5,322,902, and 5,346,925, for example, describe two-stage processes for producing propylene block copolymers. The propylene/ethylene copolymer portion of these compositions is a non-crystalline, rubbery material suitable for molding applications rather than fibers and fabrics.
This invention is directed toward a fiber comprising a crystalline propylene polymer composition comprising: a) from about 10 to about 90 weight percent crystalline, isotactic propylene homopolymer having a molecular weight distribution of less than about 3; and b) from about 90 to about 10 weight percent crystalline propylene copolymer having a molecular weight distribution of less than about 3, wherein the weight percent of the comonomer based on the total weight of the polymer is in the range of from about 0.05 to about 15.
This invention is also directed toward a fabric comprising a crystalline propylene polymer composition comprising: a) from about 10 to about 90 weight percent crystalline, isotactic propylene homopolymer having a molecular weight distribution of less than about 3; and b) from about 90 to about 10 weight percent crystalline propylene copolymer having a molecular weight distribution of less than about 3, wherein the weight percent of the comonomer based on the total weight of the polymer is in the range of from about 0.05 to about 15.
As used herein xe2x80x9ccrystallinexe2x80x9d is defined as having one or more identifiable peak melting points above about 100xc2x0 C. as determined by Differential Scanning Calorimetry (DSC peak melting temperatures).
As used herein, xe2x80x9cisotacticxe2x80x9d is defined as having at least 40% isotactic pentads according to analysis by 13C-NMR. As used herein, xe2x80x9chighly isotacticxe2x80x9d is defined as having at least 60% isotactic pentads according to analysis by 13C-NMR.
As used herein, xe2x80x9cmolecular weightxe2x80x9d means weight average molecular weight (Mw) and xe2x80x9cmolecular weight distribution,xe2x80x9d (MWD), means Mw divided by number average molecular weight (Mn).
As used herein, unless differentiated, xe2x80x9cpolymerizationxe2x80x9d includes copolymerization and terpolymerization, xe2x80x9cmonomerxe2x80x9d includes comonomer and termonomer, and xe2x80x9cpolymerxe2x80x9d includes copolymer and terpolymer.
As used herein the term xe2x80x9cfabricxe2x80x9d includes woven fabrics, nonwoven fabrics, such as spunbond and meltblown fabrics, composite fabrics and fabric laminates.
Methods for Making Crystalline Propylene Polymer Compositions
The methods of this invention involve the use of metallocene catalyst systems that comprise at least one metallocene and at least one activator. Preferably, these catalyst system components are supported on a support material.
Metallocenes
As used herein xe2x80x9cmetallocenexe2x80x9d refers generally to compounds represented by the formula CpmMRnXq wherein Cp is a cyclopentadienyl ring which may be substituted, or derivative thereof which may be substituted, M is a Group 4, 5, or 6 transition metal, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, R is a hydrocarbyl group or hydrocarboxy group having from one to 20 carbon atoms, X is a halogen, and m=1-3, n=0-3, q=0-3, and the sum of m+n+q is equal to the oxidation state of the transition metal.
Methods for making and using metallocenes are very well known in the art. For example, metallocenes are detailed in U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910; 4,808,561; 4,871,705; 4,933,403; 4,937,299; 5,017,714; 5,026,798; 5,057,475; 5,120,867; 5,278,119; 5,304,614; 5,324,800; 5,350,723; and 5,391,790 each fully incorporated herein by reference.
Preferred metallocenes are those represented by the formula: 
wherein M is a metal of Group 4, 5, or 6 of the Periodic Table preferably, zirconium, hafnium and titanium, most preferably zirconium;
R1 and R2 are identical or different, preferably identical, and are one of a hydrogen atom, a C1-C10 alkyl group, preferably a C1-C3 alkyl group, a C1-C10 alkoxy group, preferably a C1-C3 alkoxy group, a C6-C10 aryl group, preferably a C6-C8 aryl group, a C6-C10 aryloxy group, preferably a C6-C8 aryloxy group, a C2-C10 alkenyl group, preferably a C2-C4 alkenyl group, a C7-C40 arylalkyl group, preferably a C7-C10 arylalkyl group, a C7-C40 alkylaryl group, preferably a C7-C12 alkylaryl group, a C8-C40 arylalkenyl group, preferably a C8-C12 arylalkenyl group, or a halogen atom, preferably chlorine;
R3 and R4 are hydrogen atoms;
R5 and R6 are identical or different, preferably identical, are one of a halogen atom, preferably a fluorine, chlorine or bromine atom, a C1-C10 alkyl group, preferably a C1-C4 alkyl group, which may be halogenated, a C6-C10 aryl group, which may be halogenated, preferably a C6-C8 aryl group, a C2-C10 alkenyl group, preferably a C2-C4 alkenyl group, a C7-C40-arylalkyl group, preferably a C7-C10 arylalkyl group, a C7-C40 alkylaryl group, preferably a C7-C12 alkylaryl group, a C8-C40 arylalkenyl group, preferably a C8-C12 arylalkenyl group, a xe2x80x94NR215, xe2x80x94SR15, xe2x80x94OR15, xe2x80x94OSiR315 or xe2x80x94PR215 radical, wherein R15 is one of a halogen atom, preferably a chlorine atom, a C1-C10 alkyl group, preferably a C1-C3 alkyl group, or a C6-C10 aryl group, preferably a C6-C9 aryl group; 
xe2x80x94B(R11)xe2x80x94, xe2x80x94Al(R11)xe2x80x94, xe2x80x94Gexe2x80x94, xe2x80x94Snxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94N(R11)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94P(R11)xe2x80x94, or xe2x80x94P(O)(R11)xe2x80x94;
wherein:
R11, R12 and R13 are identical or different and are a hydrogen atom, a halogen atom, a C1-C20 alkyl group, preferably a C1-C10 alkyl group, a C1-C20 fluoroalkyl group, preferably a C1-C10 fluoroalkyl group, a C6-C30 aryl group, preferably a C6-C20 aryl group, a C6-C30 fluoroaryl group, preferably a C6-C20 fluoroaryl group, a C1-C20 alkoxy group, preferably a C1-C10 alkoxy group, a C2-C20 alkenyl group, preferably a C2-C10 alkenyl group, a C7-C40 arylalkyl group, preferably a C7-C20 arylalkyl group, a C8-C40 arylalkenyl group, preferably a C8-C22 arylalkenyl group, a C7-C40 alkylaryl group, preferably a C7-C20 alkylaryl group or R11 and R12, or R11 and R13, together with the atoms binding them, can form ring systems;
M2 is silicon, germanium or tin, preferably silicon or germanium, most preferably silicon;
R8 and R9 are identical or different and have the meanings stated for R11;
m and n are identical or different and are zero, 1 or 2, preferably zero or 1, m plus n being zero, 1 or 2, preferably zero or 1; and
the radicals R10 are identical or different and have the meanings stated for R11, R12 and R13. Two adjacent R10 radicals can be joined together to form a ring system, preferably a ring system containing from about 4-6 carbon atoms.
Alkyl refers to straight or branched chain substituents. Halogen (halogenated) refers to fluorine, chlorine, bromine or iodine atoms, preferably fluorine or chlorine.
Particularly preferred metallocenes are compounds of the structures (A) and (B): 
wherein:
M1 is Zr or Hf, R1 and R2 are methyl or chlorine, and R5, R6 R8, R9,R10, R11 and R12 have the above-mentioned meanings.
These chiral metallocenes may be used as a racemate for the preparation of highly isotactic polypropylene copolymers. It is also possible to use the pure R or S form. An optically active polymer can be prepared with these pure stereoisomeric forms. Preferably the meso form of the metallocene is removed to ensure the center (i.e., the metal atom) provides stereo regular polymerization. Separation of the stereoisomers can be accomplished by known literature techniques. For special products it is also possible to use rac/meso mixtures.
Additional methods for preparing metallocenes are fully described in the Journal of Organometallic Chem., volume 288, (1985), pages 63-67, and in EP-A-320762, both of which are herein fully incorporated by reference.
Illustrative but non-limiting examples of preferred metallocenes include:
Dimethylsilandiylbis (2-methyl-4-phenyl-1-indenyl)ZrCl2 
Dimethylsilandiylbis(2-methyl-4,5-benzoindenyl)ZrCl2;
Dimethylsilandiylbis(2-methyl-4,6-diisopropylindenyl)ZrCl2;
Dimethylsilandiylbis(2-ethyl-4-phenyl-1-indenyl)ZrCl2;
Dimethylsilandiylbis(2-ethyl-4-naphtbyl-1-indenyl)ZrCl2,
Phenyl(methyl)silandiylbis(2-methyl-4-phenyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4-(12-naphthyl)-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4-(2-naphthyl)-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4,5-diisopropyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2,4,6-trimethyl-1-indenyl)ZrCl2,
Phenyl(methyl)silandiylbis(2-methyl-4,6-diisopropyl-1-indenyl)ZrCl2,
1,2-Ethandiylbis(2-methyl-4,6-diisopropyl-1-indenyl)ZrCl2,
1,2-Butandiylbis(2-methyl-4,6-diisopropyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4-ethyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4-isopropyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4-t-butyl-1-indenyl)ZrCl2,
Phenyl(methyl)silandiylbis(2-methyl-4-isopropyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-ethyl-4-methyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2,4-dimethyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4-ethyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-xcex1-acenaphth-1-indenyl)ZrCl2,
Phenyl(methyl)siandiylbis(2-mehyl-ethyl-4,5-benzo-1-indenyl)ZrCl2,
Phenyl(methyl)silandiylbis(2-methyl-4,5-(methylbenzo)-1-indenyl)ZrCl2 ,
Phenyl(methyl)silandiylbis(2-methyl-4,5-(tetramethylbenzo)-1-indenyl)ZrCl2 ,
Phenyl(methyl)silandiylbis(2-methyl-a-acenaphth-1-indenyl)ZrCl2,
1,2-Ethandiylbis(2-methyl-4,5-benzo-1-indenyl)ZrCl2,
1,2-Butandiylbis(2-methyl-4,5-benzo-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-4,5-benzo-1-indenyl)ZrCl2,
1,2-Ethandiylbis(2,4,7-trimethyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-1-indenyl)ZrCl2,
1,2-Ethandiylbis(2-methyl-1-indenyl)ZrCl2,
Phenyl(methyl)silandiylbis(2-methyl-1-indenyl)ZrCl2,
Diphenylsilandiylbis(2-methyl-1-indenyl)ZrCl2,
1,2-Butandiylbis(2-methyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-ethyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-5-isobutyl-1-indenyl)ZrCl2,
Phenyl(methyl)silandiylbis(2-methyl-5-isobutyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2-methyl-5-t-butyl-1-indenyl)ZrCl2,
Dimethylsilandiylbis(2,5,6-trimethyl-1-indenyl)ZrCl2, and the like.
These preferred metallocene catalyst components are described in detail in U.S. Pat. Nos. 5,145,819; 5,243,001; 5,239,022; 5,329,033; 5,296,434; 5,276,208; and 5,374,752; and EP 549 900 and 576 970 all of which are herein fully incorporated by reference.
The metallocenes preferably selected for use in this invention are at least one metallocene catalyst system capable of producing isotactic, crystalline propylene polymer. If two metallocenes are used, then particularly preferred metallocenes are those selected from formulas A and/or B which when used alone to produce propylene homopolymer, are capable of producing an isotactic polymer having a weight average molecular weight of from about 25,000 to about 1,500,000 at commercially attractive temperatures of from about 50xc2x0 C. to about 120xc2x0 C. For some applications it is preferable to select two or more metallocenes which produce polymers having different molecular weights. This results in a broader molecular weight distribution.
Thus preferably at least one metallocene is selected from the group consisting of rac-: dimethylsilandiylbis(2-methylindenyl)zirconium dichloride; dimethylsilandiylbis(2,4-dimethylindenyl)zirconium dichloride; dimethylsilandiylbis(2,5,6-trimethylindenyl)zirconium dichloride; dimethylsilandiylbis indenyl zirconium dichloride; dimethylsilandiylbis(4,5,6,7-tetrahydroindenyl)zirconium dichloride and dimethylsilandiylbis(2-methyl-4,5-benzoindenyl)zirconium dichloride; dimethylsilandiylbis(2-methyl-4-phenylindenyl)zirconium dichloride; dimethylsilandiylbis(2-methyl-4,6-diisopropylindenyl)zirconium dichloride; dimethylsilandiylbis(2-methyl-4-napthylindenyl)zirconium dichloride; and dimethylsilandiylbis(2-ethyl-4-phenylindenyl)zirconium dichloride.
If two metallocenes are used, their ratio will depend partly on the activities of the metallocenes and on the desired contribution of each. Thus, for example, if two metallocenes are used in a 1:1 ratio and the activities of each are similar, then the polymer product will be expected to comprise about 50% of polymer produced by one metallocene and about 50% of polymer produced by the other. The breadth of the product""s molecular weight distribution will depend at least partly on the difference in molecular weight capability between the metallocenes. The addition of comonomer and/or hydrogen in the polymerization process may affect the contribution of each metallocene as described in detail below.
Activators
Metallocenes are generally used in combination with some form of activator in order to create an active catalyst system. The term xe2x80x9cactivatorxe2x80x9d is defined herein to be any compound or component, or combination of compounds or components, capable of enhancing the ability of one or more metallocenes to polymerize olefins to polyolefins. Alklyalumoxanes are preferably used as activators, most preferably methylalumoxane (MAO). Generally, the alkylalumoxanes preferred for use in olefin polymerization contain about 5 to 40 of the repeating units: 
where R is a C1-C8 alkyl including mixed alkyls. Particularly preferred are the compounds in which R is methyl. Alumoxane solutions, particularly methylalumoxane solutions, may be obtained from commercial vendors as solutions having various concentrations. There are a variety of methods for preparing alumoxane, non-limiting examples of which are described in U.S. Pat. Nos. 4,665,208, 4,952,540, 5,091,352, 5,206,199, 5,204,419, 4,874,734, 4,924,018, 4,908,463, 4,968,827, 5,308,815, 5,329,032, 5,248,801, 5,235,081, 5,157,137, 5,103,031, 5,329,032, 5,416,229, 5,391,793 and EP-B1-0 279 586, EP-B1-0 287 666 and EP-B1-0 406 912, each fully incorporated herein by reference. (as used herein unless otherwise stated xe2x80x9csolutionxe2x80x9d refers to any mixture including suspensions.)
Some MAO solutions tend to become cloudy and gelatinous over time. It may be advantageous to clarify such solutions prior to use. A number of methods are used to create gel-free MAO solutions or to remove gels from the solutions. Gelled solutions are often simply filtered or decanted to separate the gels from the clear MAO. U.S. Pat. No. 5,157,137, for example, discloses a process for forming clear, gel-free solutions of alkylalumoxane by treating a solution of alkylalumoxane with an anhydrous salt and/or hydride of an alkali or alkaline earth metal.
Ionizing activators may also be used to activate metallocenes. These activators are neutral or ionic, or are compounds such as tri(n-butyl)ammonium tetrakis(pentaflurophenyl)boron, which ionize the neutral metallocene compound. Such ionizing compounds may contain an active proton, or some other cation associated with but not coordinated or only loosely coordinated to the remaining ion of the ionizing compound. Combinations of activators may also be used, for example, alumoxane and ionizing activators in combinations, see for example, EP-B1-0 662 979.
Descriptions of ionic catalysts for coordination polymerization comprised of metallocene cations activated by non-coordinating anions appear in the early work in EP-A-0 277 004, EP-B1-0 672 688, EP-B1-0 551 277 and U.S. Pat. Nos. 5,198,401, 5,278,119, 5,407,884, 5,483,014 (incorporated herein by reference). These teach a preferred method of preparation wherein metallocenes (bisCp and monoCp) are protonated by an anion precursor such that an alkyl/hydride group is abstracted from a transition metal to make it both cationic and charge-balanced by the non-coordinating anion.
The term xe2x80x9cnoncoordinating anionxe2x80x9d means an anion which either does not coordinate to said cation or which is only weakly coordinated to said cation thereby remaining sufficiently labile to be displaced by a neutral Lewis base. xe2x80x9cCompatiblexe2x80x9d noncoordinating anions are those which are not degraded to neutrality when the initially formed complex decomposes. Further, the anion will not transfer an anionic substituent or fragment to the cation so as to cause it to form a neutral four coordinate metallocene compound and a neutral by-product from the anion. Noncoordinating anions useful in accordance with this invention are those which are compatible, stabilize the metallocene cation in the sense of balancing its ionic charge in a +1 state, yet retain sufficient lability to permit displacement by an ethylenically or acetylenically unsaturated monomer during polymerization.
The use of ionizing ionic compounds not containing an active proton but capable of producing the both the active metallocene cation and a noncoordinating anion is also known. See, EP-B1-0 426 637 and EP-A3-0 573 403 (incorporated herein by reference). An additional method of making the ionic catalysts uses ionizing anion pre-cursors which are initially neutral Lewis acids but form the cation and anion upon ionizing reaction with the metallocene compounds, for example the use of tris(pentafluorophenyl) boron. See EP-B1-0 520 732 (incorporated herein by reference). Ionic catalysts for addition polymerization can also be prepared by oxidation of the metal centers of transition metal compounds by anion pre-cursors containing metallic oxidizing groups along with the anion groups, see EP-B1-0 495 375 (incorporated herein by reference).
Where the metal ligands include halogen moieties (for example, bis-cyclopentadienyl zirconium dichloride) which are not capable of ionizing abstraction under standard conditions, they can be converted via known alkylation reactions with organometallic compounds such as lithium or aluminum hydrides or alkyls, alkylalumoxanes, Grignard reagents, etc. See EP-A4-0 500 944 and EP-B1-0 570 982 and U.S. Pat. No. 5,434,115 (incorporated herein by reference) for in situ processes describing the reaction of alkyl aluminum compounds with dihalo-substituted metallocene compounds prior to or with the addition of activating anionic compounds.
Support Materials
The catalyst systems used in the process of this invention are preferably supported using a porous particulate material, such as for example, talc, inorganic oxides, inorganic chlorides and resinous materials such as polyolefin or polymeric compounds.
The most preferred support materials are porous inorganic oxide materials, which include those from the Periodic Table of Elements of Groups 2, 3, 4, 5, 13 or 14 metal oxides. Silica, alumina, silica-alumina, and mixtures thereof are particularly preferred. Other inorganic oxides that may be employed either alone or in combination with the silica, alumina or silica-alumina are magnesia, titania, zirconia, and the like.
Preferably the support material is porous silica which has a surface area in the range of from about 10 to about 700 m2/g, a total pore volume in the range of from about 0.1 to about 4.0 cc/g and an average particle size in the range of from about 10 to about 500 xcexcm. More preferably, the surface area is in the range of from about 50 to about 500 m2/g, the pore volume is in the range of from about 0.5 to about 3.5 cc/g and the average particle size is in the range of from about 20 to about 200 xcexcm. Most preferably the surface area is in the range of from about 100 to about 400 m2/g, the pore volume is in the range of from about 0.8 to about 3.0 cc/g and the average particle size is in the range of from about 30 to about 100 xcexcm. The average pore size of typical porous support materials is in the range of from about 10 to about 1000 xc3x85. Preferably, a support material is used that has an average pore diameter of from about 50 to about 500 xc3x85, and most preferably from about 75 to about 350 xc3x85. It may be particularly desirable to dehydrate the silica at a temperature of from about 100xc2x0 C. to about 800xc2x0 C. anywhere from about 3 to about 24 hours.
The metallocene(s), activator and support material may be combined in any number of ways. Suitable support techniques are described in U.S. Pat. Nos. 4,808,561 and 4,701,432 (each fully incorporated herein by reference.). Preferably the metallocene(s) and activator are combined and their reaction product supported on the porous support material as described in U.S. Pat. No. 5,240,894 and WO 94/28034, WO 96/00243, and WO 96/00245 (each fully incorporated herein by reference.) Alternatively, the metallocene(s) may be preactivated separately and then combined with the support material either separately or together. If metallocenes are separately supported, then preferably, they are dried then combined as a powder before use in polymerization.
Regardless of whether the metallocene(s) and activator are separately precontacted or whether the metallocene(s) and activator are combined at once, the total volume of reaction solution applied to porous support is preferably less than about 4 times the total pore volume of the porous support, more preferably less than about 3 times the total pore volume of the porous support and even more preferably in the range of from more than about 1 to less than about 2.5 times the total pore volume of the porous support. Procedures for measuring the total pore volume of porous support are well known in the art. The preferred method is described in Volume 1, Experimental Methods in Catalyst Research, Academic Press, 1968, pages 67-96.
Methods of supporting ionic catalysts comprising metallocene cations and noncoordinating anions are described in EP-B1-0 507 876 and U.S. Pat. No. 5,643,847 and WO 94/03506. The methods generally comprise either physical adsorption on traditional polymeric or inorganic supports that have been largely dehydrated and dehydroxylated, or using neutral anion precursors that are sufficiently strong Lewis acids to activate retained hydroxy groups in silica containing inorganic oxide supports such that the Lewis acid becomes covalently bound and the hydrogen of the hydroxy group is available to protonate the metallocene compounds.
The supported catalyst system may be used directly in polymerization or the catalyst system may be prepolymerized using methods well known in the art. For details regarding prepolymerization, see U.S. Pat. Nos. 4,923,833 and 4,921,825, EP 0 279 863 and EP 0 354 893 each of which is fully incorporated herein by reference.
Polymerization Processes
The polymer compositions of this invention are generally prepared in a multiple stage process wherein homopolymerization and copolymerization are conducted separately in parallel or, preferably in series. In a preferred mode, propylene is homopolymerized and thereafter propylene and comonomer are copolymerized in the presence of the initially produced homopolymer using the above described metallocene catalyst systems. If, however, the copolymer is prepared first, the subsequently prepared xe2x80x9chomopolymerxe2x80x9d is likely to contain some traces of comonomer.
Individually, each stage may involve any process including gas, slurry or solution phase or high pressure autoclave processes. Preferably a slurry (bulk liquid propylene) polymerization process is used in each stage.
A slurry polymerization process generally uses pressures in the range of from about 1 to about 100 atmospheres (about 0.1 to about 10 MPa) or even greater and temperatures in the range of from xe2x88x9260xc2x0 C. to about 150xc2x0 C. In a slurry polymerization, a suspension of solid, particulate polymer is formed in a liquid or supercritical polymerization medium to which propylene and comonomers and often hydrogen along with catalyst are added. The liquid employed in the polymerization medium can be, for example, an alkane or a cycloalkane. The medium employed should be liquid under the conditions of polymerization and relatively inert such as hexane and isobutane. In the preferred embodiment, propylene serves as the polymerization diluent and the polymerization is carried out using a pressure of from about 200 kPa to about 7,000 kPa at a temperature in the range of from about 50xc2x0 C. to about 120xc2x0 C.
The periods of time for each stage will depend upon the catalyst system, comonomer and reaction conditions. In general, propylene should be homopolymerized for a time period sufficient to yield a composition having from about 10 to about 90 weight percent homopolymer based on the total weight of the polymer, preferably from about 20 to about 80 weight percent, even more preferably from about 30 to about 70 homopolymer weight percent based on the total weight of the polymer.
The polymerization may be conducted in batch or continuous mode and the entire polymerization may take place in one reactor or, preferably, the polymerization may be carried out in a series of reactors. If reactors in series are used, then the comonomer may be added to any reactor in the series, however, preferably, the comonomer is added to the second or subsequent reactor.
Hydrogen may be added to the polymerization system as a molecular weight regulator in the first and/or subsequent reactors depending upon the particular properties of the product desired and the specific metallocene used. When two metallocenes having different hydrogen responses are used, the addition of hydrogen will affect the molecular weight distribution of the polymer product accordingly. A preferred product form is to have the comonomer be present in the high molecular weight species of the total polymer composition to provide a favorable balance of fiber and fabric elasticity and strength combined with a broad bonding window for easy processing. Accordingly in this preferred case, the same or lower levels of hydrogen are utilized during copolymerization in the second or subsequent reactor as are used during homopolymerization in the first reacor.
Polymer Compositions
The polymer compositions of this invention are a reactor blend of isotactic crystalline propylene homopolymer and copolymer. The polymer comprises from about 10 to about 90 weight percent homopolymer based on the total weight of the polymer, preferably from about 20 to about 80 weight percent, even more preferably from about 30 to about 70 weight percent homopolymer based on the total weight of the polymer.
Any comonomer may be used to make the polymers of this invention. Preferably the comonomer is selected from the alpha-olefin group consisting of ethylene, 1-butene, 1-pentene, 1-hexene, and 1-octene. Combinations of comonomers can also be used. The most preferred of these comonomers are ethylene, 1-pentene, and 1-hexene. Diolefins and cyclic olefins may also be used.
The amount of comonomer used will depend on the type of comonomer and desired properties. The final composition may contain any amount of comonomer as long as the components of the composition remain crystalline. In general the amount of comonomer units based on the total weight of the polymer is in the range of from about 0.05 to about 15 weight percent, preferably from about 0.1 to about 10 weight percent, even more preferably from about 0.5 to about 8 weight percent, even more preferably from about 0.5 to about 5 weight percent, and most preferably 0.5 to about 2 weight percent based on the total weight of the polymer. Conversely, the polymer comprises from about 99.95 to about 85 weight percent propylene units based on the total weight of the polymer, preferably from about 99.90 to about 90 weight percent, more preferably from about 99.5 to about 92 weight percent, even more preferably from about 99.5 to about 95 weight percent, and most preferably from about 99.5 to about 98 weight percent propylene units based on the total weight of the polymer.
The polymers of this invention also retain the low extractables levels characteristic of single-site metallocene-based polymers, which are typically under 2 weight percent, preferably under 1 weight percent, as measured by 21 CFR Code of Federal Regulations 177.1520(d)(3)(ii). (1992)
The propylene polymer compositions of this invention preferably have a weight average molecular weight (Mw) that is in the range of from about 50,000 to about 500,000 preferably from about 100,000 to about 250,000, and most preferably from about 125,000 to about 200,000. These polymer compositions preferably have a melt flow rate (MFR) that is in the range of from about 1 dg/min. to about 3000 dg/min., preferably from about 5 dg/min. to about 70 dg/min., even more preferably from about 10 dg/min. to about 50 dg/min.
The polymers of this invention can be blended with other polymers, particularly with other polyolefins. Examples of such would include blends with conventional propylene polymers.
Fibers and Nonwoven Fabrics